P0174 Subaru Forester
System Too Lean (Bank 2) · Powertrain Code · High · Repair: Moderate
What is P0174?
The engine is running lean on bank 2. Same causes as P0171 but affecting the opposite cylinder bank on V-engines.
When the Subaru Forester triggers code P0174 (system too lean (bank 2)), it typically points to an issue in the powertrain system. This is a high severity code, so address it promptly to avoid further damage or safety concerns. Below you'll find the most common causes, symptoms, and repair options specific to the Subaru Forester.
This repair is rated moderate, meaning some experience and specialty tools required.
Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Subaru Forester.
Common Causes on Subaru Forester
- Intake manifold gasket leak on bank 2 of 2.5L or 2.4T Boxer
- Cracked PCV hose on passenger side of horizontally-opposed engine
- Bank 2 fuel injector failure due to heat soak on flat engine
- Vacuum leak at throttle body gasket
- Mass airflow sensor contamination from aftermarket air filter
Symptoms
- Rough idle especially when cold
- Hesitation or stumble on acceleration
- Engine surging at steady throttle
- Lean misfire under load
- Poor fuel economy
- Check engine light illuminated
Notes for Subaru Forester
Subaru Boxer engines have bank 2 on the passenger side. The horizontally-opposed layout makes heat dissipation uneven which can cause bank-specific lean conditions.